New plan for Akaroa wastewater
The Christchurch City Council is now considering drilling holes in the ground to dispose of Akaroa’s wastewater.
The practice is not widely used in New Zealand and has been criticised by an ecologist, who says better options are available.
The deep-bore injection method is the latest in a myriad of options looked at.
The council has been grappling with the issue for years and now has just two years to find a solution because a consent to discharge into Akaroa Harbour expires in 2020. An original plan to send the wastewater further into the harbour was declined by Environment Canterbury because of Nga¯ i Tahu opposition.
The deep-bore method was previously ruled out by council staff, but was now back on the table because a faulty flow meter grossly underestimated the amount of wastewater coming out of Akaroa and prompted a major rethink of the options.
Flows were more than double what was thought and previous options could not cope with the additional flows. The designs were based on 138,000 cubic metres of wastewater a year and the flows were found to be more than 300,000m3 a year.
The discovery was made in June 2017, after consultation had already finished, so another round of consultation was now planned for later this year.
The issue of how to dispose of Akaroa’s wastewater has been a controversial one on the Banks Peninsula after the council in 2016 said it was considering using land in either Robinsons Bay, Takamatua or Pompeys Pillar, 9.5 kilometres east of Akaroa, to spread treated wastewater onto pasture or kanuka trees.
The deep-bore injection method involved drilling holes in the ground below the groundwater level and below sea level. The wastewater would then disperse through fractures in the rock and eventually make its way to sea level, which could take between a few months to a few years, a report presented to residents earlier this month said.
Deep bores were now being considered as both a standalone option or in combination with the previous irrigation plans, council three waters and waste planning and delivery manager John Moore said.
The next step was to drill a test bore to determine where the water went and if that posed environmental concerns, he said. The test bore would also determine if deepbore injection was feasible. It was not known where this bore would be located.
Four wells would cost about $4 million to create, Moore said. Costs for the previous options ranged from $7.4m to $13.7m.
The deep-bore method has been used in Russell since 2000 where 85 bores of up to 35 metres deep are used to dispose of an average of
200m3 of wastewater a day from
524 properties. Robinsons Bay resident and Friends of Banks Peninsula deputy chairwoman Suky Thompson said the community still had several questions about the deep-bore injection method and was concerned about the environmental impact.
She said the council told residents the bores would be 1500m away from public water supply wells, but there had been no mention of making sure they were a certain distance away from private supply wells. This was concerning since many homes relied on spring water.